Bob Newman explains exactly why your digital camera heats up during use

One of the characteristic differences between digital cameras and their film-based predecessors is the fact that digital cameras inevitably produce heat as they operate. The heat derives directly from the operation of the camera’s electronic circuitry. Electronics generally work by modulation of an electrical property called ‘resistance’ – that is, the degree of obstruction that an electronic component offers to the flow of electrical current.

The theory is encapsulated in the well-known Ohm’s law, which states that the current through a resistive element is given by the potential (voltage) applied across it divided by the element’s ‘resistance’, measured in Ohms. Thus, an element with a small resistance will allow a large current to flow, while one with a large resistance will allow only a small current. The second electrical rule of relevance is the power equation: that the power consumed by a resistor is the voltage across it times the current passing through it, which taken along with Ohm’s law gives the square of the voltage divided by the resistance.

The result is that electronics must always draw power, which is always released in the form of heat. So an electronic camera will always produce heat as it does its work. In the case of a digital camera, the ‘modulation’ of resistance takes the form of switching the resistance between two states – ‘on’ and ‘off’. In theory, the ‘on’ resistance should be zero, and the ‘off’ resistance should be infinite. Neither of these states would use any power, since either the voltage or the current is zero. In the real world, there is no such thing as ‘zero’ or ‘infinity’, so even digital electronics will consume some power.

A bigger problem is the change of state, where the resistance of the switched element will change from ‘on’ to ‘off’, going through every state in between – and therefore potentially use power and generate heat. The power usage of a digital circuit is therefore proportional to the number of such changes of state that occur in a given time. We’d expect a camera processing very many pixels, or one with a very high frame rate, to consume more power and produce more heat.

This heat is channelled through heat-conductive structures (chunks of metal) to somewhere on the camera’s body where it can be radiated away. So why don’t modern high-pixel, high-frame-rate cameras get too hot to hold? The answer lies in improvements to the continuous semiconductor process as pixel counts have risen. This improves the quality of the switches (how perfectly they approximate ‘on’ and ‘off’) and also results in a reduction in operating voltages. Since power is proportional to the square of voltage, any reduction can have a large impact on heat produced.

This is the CMOS switching circuit that forms the basis of modern camera electronics. It consists of two transistors (Q1 and Q2) one of which is always on, the other off. In theory, while in this state it consumes no power and produces no heat. Changing between states is, however, a different story.

Bob Newman is currently Professor of Computer Science at the University of Wolverhampton. He has been working with the design and development of high-technology equipment for 35 years and two of his products have won innovation awards. Bob is also a camera nut and a keen amateur photographer