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disposable camera charging circuit Answered

why doesn't the transistor in the inverter circuit of the disposable camera ever heat up?
dont they need heat sinks?
can anybody pls show me a schematic of a simple disposable camera charging circuit? pls show the transistor number and type


A transistor normally gets hot if you reside too long in its half-switched state. as long as you traverse as fast as possible from OFF to ON or back, you waste only a very short time wasting energy. Thats because during the change from ON to OFF the transistor is (simplified spoken) a variable resistor. In its ON or OFF state, a transistor for those purposes are really good and near ideal. So in the ON state, you can push a lot of current thru without too much heat generated. in the OFF state, it blocks the current quite good and no flow of currents causes heat at all.

The problematic thing is the time you use to go from one to the other state. Keeping this time short (microsecs to nanosecs) and you get no real heat to consider...

See the first attached (simpler) graph. the heat almost only gets generated during the reguin seen to the left where the line comes from the lower left corner in a tilted straight line up. Thats where the transistor acts as resistor (Means: The more voltage the more current).

I also added a complete graph to show you the links from Ube, Ib, Ic and Uce.


Components get hot if there is electrical energy being converted to heat more quickly than it is radiated or conducted away.

If the current and voltage-drop are low, and the component has a relatively large surface area, it is less likely to heat up.

Add to that the fact that the circuit in a disposable camera is only used for a few seconds at a time, with plenty of cooling time between, and you can see that there is little reason for any part of it to heat up.

is there a way i could lower ahe amperage by adding resistors in parallel?

I assume you mean the transistor and you add them in series to the emitter or the collector.

These are some camera flash circuits the top two are disposable and the bottom
one is a Polaroid the missing circuit is in the pic.

Transistors get hot because you are putting a lot of power through it most camera flashes don’t use a lot of power.

Camera Flash 4.bmp027.JPG