Datasheet NCP1200 (ON Semiconductor) - 7

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NCP1200 APPLICATIONS INFORMATION INTRODUCTION Dynamic Self−Supply
The NCP1200 implements a standard current mode The DSS principle is based on the charge/discharge of the architecture where the switch−off time is dictated by the VCC bulk capacitor from a low level up to a higher level. We peak current setpoint. This component represents the ideal can easily describe the current source operation with a bunch candidate where low part−count is the key parameter, of simple logical equations: particularly in low−cost AC−DC adapters, auxiliary POWER−ON: IF VCC < VCCOFF THEN Current Source supplies etc. Due to its high−performance High−Voltage is ON, no output pulses technology, the NCP1200 incorporates all the necessary IF VCC decreasing > VCCON THEN Current Source is components normally needed in UC384X based supplies: OFF, output is pulsing timing components, feedback devices, low−pass filter and IF VCC increasing < VCCOFF THEN Current Source is self−supply. This later point emphasizes the fact that ON ON, output is pulsing Semiconductor’s NCP1200 does NOT need an auxiliary Typical values are: VCCOFF = 11.4 V, VCCON = 9.8 V winding to operate: the product is naturally supplied from To better understand the operational principle, Figure 15’s the high−voltage rail and delivers a VCC to the IC. This sketch offers the necessary light: system is called the Dynamic Self−Supply (DSS). VCCOFF = 11.4 V 10.6 V Avg. VCC VCCON = 9.8 V ON OFF Current Source Output Pulses 10.00M 30.00M 50.00M 70.00M 90.00M
Figure 15. The Charge/Discharge Cycle Over a 10 mF VCC Capacitor
The DSS behavior actually depends on the internal IC
.
0.16 = 256 mW. If for design reasons this contribution is consumption and the MOSFET’s gate charge, Qg. If we still too high, several solutions exist to diminish it: select a MOSFET like the MTD1N60E, Qg equals 11 nC 1. Use a MOSFET with lower gate charge Qg (max). With a maximum switching frequency of 48 kHz (for 2. Connect pin through a diode (1N4007 typically) to the P40 version), the average power necessary to drive the one of the mains input. The average value on pin 8 MOSFET (excluding the driver efficiency and neglecting 2 * Vmains PEAK various voltage drops) is: becomes p . Our power contribution example drops to: 160 mW. Fsw @ Qg @ Vcc with Fsw = maximum switching frequency Dstart Qg = MOSFET’s gate charge 1N4007 VCC = VGS level applied to the gate To obtain the final driver contribution to the IC C3 + NCP1200 consumption, simply divide this result by VCC: Idriver = 4.7 mF Fsw @ Qg = 530 mA. The total standby power consumption 400 V 1 HV Adj 8 at no−load will therefore heavily rely on the internal IC 2 FB NC 7 consumption plus the above driving current (altered by the 3 CS VCC 6 driver’s efficiency). Suppose that the IC is supplied from a EMI 4 GND Drv 5 400 V DC line. To fully supply the integrated circuit, let’s Filter imagine the 4 mA source is ON during 8 ms and OFF during
Figure 16. A simple diode naturally reduces the
50 ms. The IC power contribution is therefore: 400 V
.
4 mA
average voltage on pin 8 www.onsemi.com 7