Diodes

[trash]

No takers to explain these critters ?

Diodes.

Diodes are like one way streets for electricty or a valve for water. They let cerrent flow one way and not the other.
Or they are a open circuit in one direction and short circuit the other. Don’t short circuit them.. they tend to do bad things.

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Anode Cathode

The cathode is the end of the diode with the band on it.
That’s it, basic diodes a pretty simple devices.
Their main use is to turn AC into DC or to protect circuits.

That’s the simple stuff… now the harder stuff ….

There is also a small loss of voltage across a diode.
It is usually about 0.7 Volts, but can vary with different types of diode. The diode will not let current flow until the voltage gets
about 0.7 Volts, then it will behave normally.
It’s easy to ignore this small voltage drop, and in some cases make use of it. I usually ignore it, but it isn’t something you should overlook when using small voltages. (thanks uA !)

There are also diodes that do “other things”.

There is a diode called a “Zener”. It conduct power normally
in the forward direction, but when it is in reverse it will not
let current flow, like a normal diode, UNTIL the voltage gets to a
certain level. Then the diode behaves like a short circuit letting
current flow. These types of diodes are usually used as voltage regulators.

It can be said all diodes behave like zeners, even LED’s, but most other diodes will break if you exceed their reverse breakdown voltage.
Zener diodes will also break if you don’t protect them from current overload in reverse !

LED’s simply create light. They don’t work like a normal light globe, but more like a laser does. Generally, they need about 1.5 volts and 20mA to turn on and glow normally. This varies with each kind of LED,
so it is best to check the specs for each type.

Solar Panels are just a kind of diode. They do the reverse of an LED,
they convert light into electricity. Actually, even an normal red LED will create electricity when light shines on it. If you have a really sensitive multimeter or CRO, you can test it out.

There are many other types of diodes that you may come across.
small signal diodes, point contact, mixer diodes, varactor diodes,
regulator diodes, gunn diodes, schotky diodes, even really weird stuff like tunnel diodes. Each has some magical and wonderful property which you will be of no use to you. 🙂

The is one combination of diodes that is worth a mention. It’s a ring of four diodes called a “bridge rectifier”. It’s used for converting AC into DC. A single diode can do this itself, a bridge rectifier is just more efficient.

[betty.k]

top job as always t! i’m building a nice little electronics 101 folder:8ball:

[twizm]

thats odd, because if diodes produce light and they only work in one direction, youd think that by absorbing light they wouldnt work at all.

nice work nonetheless.:)

[betty.k]

i think what trash is saying is you run power down the anode (or cathode, not 100% on that) in a led and it produces light. if you shine light on it, it produces power back down the anode.

power + led = light
light + led = power:8ball:

[trash]

light + led = power is correct.
A tiny voltage appears across the two leads.
They work like tiny little solar panels though there isn’t enough energy to actually power anything. They do work well as light sensors.

The complementry is …
It is amusing is that solar panels don’t produce light when you apply power to them.

[twizm]

indeed it is trash. indeed it is…

[ph2t]

Fellas, to add some info:

In the receiver circuit for these cars is a DCDC convertor. The DCDC convertor is used to increase the voltage from 1.2V to 3V. The IC on the receiver pcb needs at least 2.something volts to work so that’s why it’s there.

You will notice on the unside of the pcb a little orange glass canister thingy. This is shown in the right of the picture below:

This is a diode, in particular it is probably either a gernanium (spelling?) or schottky diode. These have a lower voltage loss (as trash was eluding to earlier) than your normal silicon diodes. So instead of 0.7V, you are looking at approx 0.2V to 0.5V drop with these diodes.

Why do they use these types of diodes? We’ll it’s all about loss and minimising this. If you are using a silicon diode in the DCDC convertor circuit then you would have more loss and therefore it would be harder to maintain a higher output voltage than if you were to use a lower loss diode.

Below is a picture of a DCDC convertor circuit. This circuit is NOT the exact model of what’s on the BCG circuit but it is close.

You can see the diode in this circuit, it is this symbol .

ph2t.

Edited by – ph2t on 16 November 2003 11:34:07

Edited by – ph2t on 16 November 2003 11:36:23

[trash]

Thanks ph2t,
That’s a small switchmode boost converter.
Though I’m not sure that is what’s used.
I don’t own a real tomy, is there a small coil on there somewhere ?
You can step the voltage up to something like 3 volts and throw away 0.5V with the diode to get 2.5V. (I’m ignoring internal resistance of the diode).
I’m not a real diode whizz, I just look up the specs like everybody else and use them when needed. I can’t even remember voltage drops for Germanium diodes. But both them and Schottky diodes (0.3V) are generally used as high frequency detector or mixer diodes, usually in AM radio receivers.
The diode may be a detector diode (uA .. where’s that RX board cct diagram ?) or it may be used because it fast switching for a tiny high frequency switchmode power supply.

Interesting stuff.

[ph2t]

Actually dude the diode on the pcb IS used for the voltage boost circuit. Trust me, I’ve done the measurements and the research for this. The DCDC convertor used is ME301 and there is a 220uH inductor on the board (axial type) also there is a 100uF 6V electrolytic cap on the board as well.

During various mods I’ve actually broken the diode on the board and substituted it with another diode no sweats. You should use a shottky based one for it’s reduced voltage drop.

The NCP1402 circuit pictured above is the one I use to convert the 1.2V rail from the NiCd and boost it to 5V. From this I’ve been able to run 5 LEDs. 2 White, 2 Blue, 2 Red and 1 Yellow. Yeah!

[trash]

Hahah, classic. Can you come around, my xmas tree needs a professional touch !
yes, the mention of the coil is the smoking gun. 🙂

[jamiekulhanek]

That gloria is beautiful…

[Author]

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