Low-current power supply on linear light bulb driver SM2082D
Krenka at 220, in short. If you google this question directly, you will find a rather expensive TL783 chip. In turn, drivers from 50 ruble lamps cost either 100 rubles per package or are soldered free of charge from donors. Despite the fact that the driver is designed to stabilize the current. It is not difficult to obtain a voltage stabilizer from it. Which is what I used in a flashlight that charges from an outlet.
Why this stabilizer?
Given: an old ruble flashlight with a capacitor power supply. There is no point in talking about the stability of such a power source. A frequent breakdown of such flashlights is the LEDs burning out when plugged into an outlet. That is, they cannot charge and light at the same time. Such a flashlight will be saved by a circuit with a voltage stabilizer.
Description of the flashlight circuit.
The power supply is still capacitor, the capacitor is supported by resistors R1 – R4. They smooth out current surges when turned on, they are doubled so that there is no breakdown, double 1206 are enough for this task. R5 discharges the capacitor to prevent electric shock. After the damping capacitor there is a diode bridge and a smoothing capacitor. Because The voltage has already been reduced, then you can get by with a 100V capacitor. And so, we waited for that same stabilizer. Not usually included. A five-volt zener diode is inserted into the ground terminal of the stabilizer. And the load is turned on not between +220 and the drain (as the datasheet suggests), but between the source and ground, parallel to the zener diode. A current shunt is still needed, I was a little naughty and set the current to 80 mA instead of the allowed 60. In the future, the flashlight most economical boring. TP4056 for charging the battery, configured for a current of 80 mA and a CMOS stabilizer of 200 mA, 3.3 V instead of the current-limiting LED shunt, a pair of 10 μF ceramic capacitors. A separate board with the LEDs themselves and small shunts, just in case. A separate charging indicator board to install it in place of the flashlight indicator.
Initially, I tried the AMS1117ADJ instead of the XC6206P332. But it was upset by the voltage drop, 1.1V for 1117 versus 0.2 for 6206. As a result, it turned out that the weak voltage stabilizer 6206 rests on the current protection and works as a 200mA current stabilizer, although this is exactly the current I need.
The voltages on the board are as follows: before the capacitor 220 V, after 9 V, after SM2082 5.1 V without load and 3.8 V when a dead battery is charging, after the XC6026 stabilizer 3-3.1 V, because current protection is triggered.
The formulas are as follows:
Istab = 0.6/R8
Icharge = R9/77000
The circuit and board in kicad are on gitlab.
Result
The capacitor power supply with a light bulb stabilizer met all expectations. Now you don’t have to worry about the battery, and you don’t have to worry about burning out the LEDs from accidentally turning on the flashlight while charging. Such a low-current power supply can be useful in any cheap devices.
Operating modes are optimal. Lights for 2-3 hours from Li-ion from a 600 mAh mobile phone at a current of 200 mA. And after a dead flashlight can be charged overnight, for 10 hours with a charging current of 80 mA. Among the shortcomings, we can say about the overloaded voltage (current) stabilizer of the LEDs and the non-working red LED of the TP4056 charging indicator (apparently from a current of 80mA it does not work at all). True, all these shortcomings are covered by the low cost of this scheme. The flashlight turned out to be a little more expensive than a regular flashlight with a capacitor power supply.
