Abstract: DS3984, DS3988, DS3991, DS3992, and DS3994 are cold cathode fluorescent lamp (CCFL) controllers used for backlighting of liquid crystal display LCDs. Each controller channel can drive two logic level MOSFETs to convert the DC voltage to the high-voltage AC waveform required for CCFL driving. In some applications, power MOSFETs require greater drive capability and higher gate-source voltages, driving multiple lamps with a single channel. This application note describes how to enhance the drive capability of the DS39xx series controllers so that they can effectively drive high-power MOSFETs.
DS39xx gate drives DS3984, DS3988, DS3991, DS3992, and DS3994 controllers have two gate drives per channel. Each gate drive can drive a logic level MOSFET. The maximum output load of the gate driver is 20nC, and the high-level output voltage is about VCC (5V). This driving capability can meet the driving requirements of most logic level MOSFETs.
With the increasing physical size of LCD monitors and LCD TV monitors, many applications require each control channel to drive multiple lamps. For example, a single channel DS3991 is used to control all the lamps of a large LCD TV. In order to ensure reliable driving of multiple lamps, high-power MOSFETs are required. There are also some new applications that use very high DC input voltage (up to 400V) to reduce the operating current of LCD TVs. The CCFL power of such LCD TVs may reach 200W. These new applications also require high-voltage power MOSFETs to drive the lamps.
Power MOSFETs generally have a higher gate charge than logic level control MOSFETs. Therefore, the gate drive circuit must have a sufficiently high peak drive current to quickly charge and discharge the gate capacitance. Power MOSFETs also require higher gate-source voltages to ensure effective turn-on.
The gate drive circuit built into the DS39xx series controllers cannot directly drive high-power MOSFETs, but this problem can be solved. This application note explains how to use simple peripheral circuits to enhance the gate drive capability of the DS39xx series controllers to drive high-power MOSFETs.
Enhanced gate drive circuit Figure 1 details the enhanced drive circuit.
Figure 1. External circuit to enhance DS39xx gate drive
In Figure 1, GA and GB are the gate drive signal output of the CCFL controller. Q2 / Q3 / Q5 / Q6 are general-purpose NPN transistors used to convert the levels of GA and GB from 5V to 12V. Then the signal is driven by two totem poles composed of Q1 / Q7 and Q4 / Q8. The output drive signal is shown as GA_12V and GB_12V. When the power MOSFET is turned on, the totem pole drive circuit can quickly charge the gate capacitance; when the MOSFET is turned off, it can also quickly discharge the gate capacitance. Q1 / Q4 / Q7 / Q8 are medium power transistors used to ensure sufficient peak current. Figure 2 shows the waveforms of GA, GB, GA_12V and GB_12V.
Figure 2. Waveforms of logic level gate drive signals (GA and GB) and 12V level gate drive signals (GA_12V and GB_12V)
GA_12V and GB_12V use push-pull architecture to directly drive power MOSFETs. With some additional circuits, it can also be used for half-bridge or full-bridge drive (please contact the factory for details). Recommended Transistor Models Table 1 lists the recommended transistor models used in Figure 1.
Table 1. Recommended transistor models
DS39xx gate drives DS3984, DS3988, DS3991, DS3992, and DS3994 controllers have two gate drives per channel. Each gate drive can drive a logic level MOSFET. The maximum output load of the gate driver is 20nC, and the high-level output voltage is about VCC (5V). This driving capability can meet the driving requirements of most logic level MOSFETs.
With the increasing physical size of LCD monitors and LCD TV monitors, many applications require each control channel to drive multiple lamps. For example, a single channel DS3991 is used to control all the lamps of a large LCD TV. In order to ensure reliable driving of multiple lamps, high-power MOSFETs are required. There are also some new applications that use very high DC input voltage (up to 400V) to reduce the operating current of LCD TVs. The CCFL power of such LCD TVs may reach 200W. These new applications also require high-voltage power MOSFETs to drive the lamps.
Power MOSFETs generally have a higher gate charge than logic level control MOSFETs. Therefore, the gate drive circuit must have a sufficiently high peak drive current to quickly charge and discharge the gate capacitance. Power MOSFETs also require higher gate-source voltages to ensure effective turn-on.
The gate drive circuit built into the DS39xx series controllers cannot directly drive high-power MOSFETs, but this problem can be solved. This application note explains how to use simple peripheral circuits to enhance the gate drive capability of the DS39xx series controllers to drive high-power MOSFETs.
Enhanced gate drive circuit Figure 1 details the enhanced drive circuit.
Figure 1. External circuit to enhance DS39xx gate drive
In Figure 1, GA and GB are the gate drive signal output of the CCFL controller. Q2 / Q3 / Q5 / Q6 are general-purpose NPN transistors used to convert the levels of GA and GB from 5V to 12V. Then the signal is driven by two totem poles composed of Q1 / Q7 and Q4 / Q8. The output drive signal is shown as GA_12V and GB_12V. When the power MOSFET is turned on, the totem pole drive circuit can quickly charge the gate capacitance; when the MOSFET is turned off, it can also quickly discharge the gate capacitance. Q1 / Q4 / Q7 / Q8 are medium power transistors used to ensure sufficient peak current. Figure 2 shows the waveforms of GA, GB, GA_12V and GB_12V.
Figure 2. Waveforms of logic level gate drive signals (GA and GB) and 12V level gate drive signals (GA_12V and GB_12V)
GA_12V and GB_12V use push-pull architecture to directly drive power MOSFETs. With some additional circuits, it can also be used for half-bridge or full-bridge drive (please contact the factory for details). Recommended Transistor Models Table 1 lists the recommended transistor models used in Figure 1.
Table 1. Recommended transistor models
| Designator | DescripTIon | Suggested Part Numbers |
| Q2 / Q3 / Q5 / Q6 | NPN general-purpose transistor | MMBT3904 or equivalent |
| Q1 / Q4 | NPN medium-power transistor | FMMT493, ZXTN2038F, or equivalent |
| Q7 / Q8 | PNP medium-power transistor | FMMT593, ZXTP2039F, or equivalent |
7g Taper Color Candle also called Color Spiral Taper Candle , it is colorful and unscented,materails of Unscented Color Taper Candle is 100%paraffin waxn .also the proprotion of materails can be to your order. we make sure it is high quality with fast shipment . Color Spiral Taper Candle 's melting point is 58-60degree. if goods delivery to your country , Unscented Color Taper Candle not easily deformed. it have six colors. such as red ,green,blue,yellow,organe. red candle called Red Color Taper Candle. Brand can do your own brand .
Welcome to new and old customer to inquiry and order .we always online waiting your repoponse. all the clients are our important person.
7G Taper Color Candle
7G Taper Color Candle,Color Spiral Taper Candle,Red Color Taper Candle,Unscented Color Taper Candle
Shijiazhuang Zhongya Candle Co,. Ltd. , https://www.zycandlefactory.com